A vehicle grille is typically located at a front end of a vehicle, and can be configured to provide an opening through with intake air is received from outside of the vehicle, such as a grille opening or bumper opening. Such intake air may then be directed to an engine compartment of the vehicle to assist the vehicle's cooling system in cooling the engine, transmission, and other such components of the engine compartment. Such air flow via the grille may add aerodynamic drag when the vehicle is in motion. Accordingly, grilles may include grille shutters to block such air flow, thus reducing aerodynamic drag and improving fuel economy. Closed grille shutters may also provide a faster powertrain warm-up which may improve fuel economy since there is less friction, and may improve the performance of the passenger compartment heater. However, closed grille shutters also reduce the air flow through the radiator and other components for cooling purposes. As a result, engine temperatures such as engine coolant temperature (ECT) may increase. Thus, grille shutter operation may include increasing or decreasing the opening of the grille shutters based on engine cooling demands and vehicle driving conditions.
One example approach for adjusting grille shutters is shown by Kerns et al. in U.S. Pat. No. 8,311,708. Therein, vehicle grille shutters are adjusted in response to engine temperature and a non-driven vehicle condition. For example, when engine temperature is above a threshold temperature, the grille shutters may be opened.
However, the inventors herein have recognized potential issues with such systems. As one example, fully opening the grille shutters responsive to a threshold engine temperature may increase the opening of the grille shutters more than necessary, thereby reducing vehicle fuel economy. However, not opening the grille shutters soon enough (at the appropriate threshold) may cause engine temperatures to increase, thereby degrading engine performance. Further, during use the grille shutters may become incorrectly calibrated such that an actual position of the grille shutters may be different than the commanded position. As a result of degraded position control, engine temperatures (e.g., ECT) may increase, thereby resulting in degraded engine operation. For example, if grille shutters are not fully opened when commanded, ECT may increase and reduce engine cooling provided by the radiator.
In one example, the issues described above may be addressed by a method for during a first condition, adjusting grille shutters based on engine coolant temperature (ECT) and additional engine operating conditions and during a second condition when ECT is greater than a threshold temperature, adjusting the grille shutters from a partially open position based on ECT independent of the additional engine operating conditions. In this way, the grille shutters may be maintained at least partially open to aid in engine cooling when the ECT is greater than the threshold temperature. As a result, ECT may be decreased while also reducing the effect on fuel economy.
As one example, an engine controller may determine a commanded position of the grille shutters and then adjust a motor coupled to the grille shutters to move the grille shutters into the commanded position. When ECT is at or below the threshold temperature, the engine controller may adjust the grille shutters based on ECT and additional engine operating conditions, the additional engine operating conditions including one or more of a vehicle driving condition, pedal position, charge air cooler efficiency, charge air cooler temperature, or vehicle speed. Alternatively, when ECT is above the threshold temperature, the engine controller may determine a percentage opening of the grille shutters as a function of only ECT and then adjust the grille shutters to the determined percentage opening. The percentage opening may be between the partially open position and a maximal percentage opening, the percentage opening increasing with increasing ECT. In one example, the partially open position may be a percentage opening of 10% and the maximal percentage opening may be a percentage opening of 100%.
Further, during operation when ECT is above the threshold temperature, the engine controller may verify the position of the grille shutters. For example, after adjusting the grille shutters to the maximal percentage opening, the engine controller may adjust the grille shutters to a secondary percentage opening and then back to the maximal percentage opening, the secondary percentage opening smaller than the maximal percentage opening. The engine controller may then indicate degradation of the grille shutters and set an out of position flag if a stall current is not detected upon adjusting the grille shutters back to the maximal percentage opening from the secondary percentage opening. The stall current may be produced by the grille shutters contacting an end stop upon reaching the maximal percentage opening. When the ECT decreases back below the threshold temperature, the controller may then recalibrate the grille shutters if the out of position flag was set.
Recalibration of the grille shutters may also be initiated by the engine controller when a position error increases above a threshold. For example, the controller may determine the grille shutter position error based on a difference between the commanded position and a feedback position. The feedback position may be based on an output from a grille shutter position sensor. In this way, if grille shutter position control is degraded, recalibration may reset the grille shutter position and increase accuracy of the commanded grille shutter position. As a result, the desired cooling may be provided while also increasing vehicle fuel economy.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.